How to solve window manager problem in Linux Mint 14 (Xfce) after installing LXDE?

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http://unix.stackexchange.com – I like the way Xfce works on top of Linux Mint 14 Nadia (Quantal) - but I also like LXDE that I want to have in parallel. Mint 14 has no LXDE "version" now, and that is too bad. I heard that installing multiple DE is not a problem. But ... problems may occur. After installing LXDE (and I am not sure this is the real cause of that), when I log in Xfce (which is the main "flavour" of my Linux Mint installation) all windows are missing the upper frame and buttons, and are stuck to the upper border of the screen. Alt-Tab would not work. Reinstalling Xfwm4 didn't help. LXDE behaves just fine - (HowTos)